Dear folks,

I would like to compare two unequal matrices. At the moment I realize 
this with two for loop and an if function but that's definitely too slow 
:(...

Here is my code:

for (i in 1:length(all_expressed_genes[,1])) {
   for (j in 1:length(kegg_gene_pVal[,1])) {
     if (all_expressed_genes[j,1] == kegg_gene_pVal[i,1]) {
       kegg_gene_pVal[j,4] =  all_expressed_genes[i,6]
     }
   }
}

Are there any faster solutions for that easy code? And why is R so 
dramatically slow when using for, while or other loop functions?

Thanks in advance,
Paul




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